Though CT exams represent a small percentage of radiological examinations, they result in a significant portion of the radiation dose received by patients from medical procedures. Recent advances in technology have increased both the capability and utilization of CT. Concerns about the widespread use of CT, and specifically their increased utilization in the pediatric population, have arisen because of radiation dose issues. In response to these concerns, CT manufacturers have responded with methods to reduce dose such as tube current modulation techniques. However, current methods for estimating the radiation dose to patients are based either on cylindrical phantoms or on Monte Carlo simulations based on an anthropomorphic mathematical model of standard adult size using scanners in use prior to the introduction of helical or multidetector CT (MDCT). Thus, current methods to estimate radiation dose from CT exams either do not take into account characteristics of current scanners, their capabilities (e.g. tube current modulation) or the effect of patient size. The long term goal of this research is to create methods to accurately estimate radiation dose to patients undergoing CT scanning. We propose a comprehensive Monte Carlo-based modeling approach that overcomes the limitations of previous methods by accurately modeling MDCT source characteristics, the effects of different scan parameters and realistic patient models of different sizes, ages and genders. To perform this research, we propose a consortium of collaborators who bring together the expertise in both modeling and measurement of radiation dose that will be necessary to develop methods for accurate assessment of patient radiation dose from CT. The specific aims of this research are: (1) To extend the Monte Carlo model previously developed to take into account MDCT characteristics and the effects of scan parameters, (2) To verify the model using measurements, made in cylindrical acrylic and anthropomorphic tissue equivalent phantoms; (3) To continue the model verification using measurements made on patients of different sizes; (4) To estimate the absolute dose to critical organs from various imaging protocols using models of pediatric and adult patients and (5) to generalize this approach based on physical measurements so that accurate radiation dose estimates.can be obtained without performing all aspects of the detailed analysis and modeling. [unreadable] [unreadable]